GRB 051221A
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(detected 21 December 2005)
 | |
| Event type | Gamma-ray burst |
|---|---|
| Date | c. 5 billion years ago (detected 21 December 2005) |
| Duration | c. 1.4 seconds |
| Instrument | Swift |
| Constellation | Pegasus |
| Distance | c. 5 billion ly |
| Redshift | 0.5464 |
| Other designations | GRB 051221, GRB 051221A |
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GRB 051221A was a gamma ray burst (GRB) that was detected by NASA's Swift Gamma-Ray Burst Mission on December 21, 2005. The coordinates of the burst were α=21h 54m 50.7s, δ=16° 53′ 31.9″, and it lasted about 1.4 seconds.[1] The same satellite discovered X-ray emission from the same object, and the GMOS Instrument on the Gemini Observatory discovered an afterglow in the visible spectrum. This was observed for the next ten days, allowing a redshift of Z = 0.5464 to be determined for the host galaxy.[2]
The gamma ray emission from this object is of the variety known as a short-hard burst. The energy emission is consistent with the model of a merger by compact objects. It was the most distant short-hard burst found to that date for which a redshift could be determined.[2] The X-ray light curve showed evidence of three distinct breaks, possibly representing a strong energy injection.[3] The energy may have been injected by a millisecond magnetar. That is, a rapidly rotating pulsar with a strong magnetic field, estimated at 1014 gauss (1010 teslas).[4]